Driving unit for sound reproducers



Aug. 16, 1932. RlNGEL 1,871,739

DRIVING UNIT FOR SOUNDREPRODUOEKS Filed April 5. 1928 AT ORNEY Patented Aug. 16, 1932 1,871,739

UNITED STATES PATENT OFFICE RING-EL, OI BROOKLYN, NEW YORK, ASSIGNOR T0 RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE DRIVING UNIT FOR SOUND REPBODUCERS Application filed April 5, 1928. Serial No. 267,533.

This invention relates to an electro-magnetic type of driving unit such as is frequently used for operating loud speakers of the type that radiate directly to the open air. More particularly, it relates to the balanced armature type of electro-magnetic driving unit and to a means for damping the armature vibrations and limiting the amplitude of armature movement.

In the balanced armature type of driving unit, as is well known in the art, the stiffness of the armature spring is often counter-balanced or even altogether nullified by the action of the permanent magnetic poles. As a result the armature moves to engage the pole piece upon a very slight impulse and tends to stick to the poles. This is very objectionable as it destroys the balanced feature of the driving unit and in some cases actually prevents further motion of the armature. Also, it is apt to result in the soft iron armature becoming permanently polarized or magnetically saturated with the operation of the driving unit thus being materially changed. In cases where the soft iron armature becomes polarized or magnetically saturated the wave shape of the magnetization of the armature is quite different from the wave shape of the original magnetizing current in the coils. This causes a distorted motion of the armature.

When this t pe of driving unit is used in combination with a diaphragm, such as a cone that radiates directly to the open air, the moving parts have a natural resonance frequency which is within the audible frequency range. These moving parts, which include the armature, the armature spring, the cone diaphragm and the members connecting the diaphragm with the armature, are known as the vibrating system. This natural resonance is objectionable. in that it causes an excessive reproduction of sound in the region of the resonance frequency. I have found that this natural resonance can be damped by yieldingly limiting the amplitude of the armature movement.

It is an object of my invention to provide a means for preventing the armature of a balanced armature type of electro-magnetic driving unit from sticking to the pole pieces of the driving unit, and for preventing the armature from being too easily attracted to one of the pole pieces by a small energy impulse so that the armature will not become magnetically saturated and the armature motion distorted.

Another object of my invention is to provide a means for damping the natural resonance of the vibrating system, so that the resonant frequencies are not unduly stressed in the reproduction of sound.

I have also found that by limiting the amplitude of motion of the armature, so that it cannotstrike the pole pieces, it is possible to use a much weaker restraining spring on the armature. By this means, the fundamental resonance of the vibrating system is reduced to a considerably lower frequency, enabling the system to vibrate more easily and therefore radiate more sound at lower freqeuncies, thus increasing the fidelity of the receiver.

It is a still further object of my invention to provide a vibrating system employing a much weaker spring than it has heretofore been possible to use and at the same time prevent the armature from sticking to the pole pieces.

These objects and others which will become apparent upon reading the following specification in connection with the accompanying drawing, are attained by providing a yielding member or members to engage the armature and yieldingly limit its movement in both directions.

n the accompanying drawing which shows an approved form of my invention and a. modification thereof, Fig. 1 is a sectional view of a balanced armature type of electro-magnetic driving unit to which one form of my invention has been added; Fig. 2 is a section taken on line 22 of Fig. 1, and Fig. 3 is a sectional view corresponding to Fig. 1, illustrating another modification of my invention.

Referring more particularly to the drawing, reference character -1 indicates a soft iron pole piece which is connected to the 'north pole of a permanent U shaped magnet M. A similar pole piece 2 is connected to the south pole of the same permanent magnet.

These pole pieces which are each forked to provide two points of like polarity indicated as N, N and S, S are positioned to form two gaps suflicientlylarge to receive a soft iron armature 3. The armature 3 is suspended to vibrate in these gaps between the points N, S and N, S by means of a phosphor bronze spring 4, in a manner well known in the art.

Two coils 5 are mounted around the arma ture 3 and within the pole pieces 1 and 2. These coils are adapted to be connected to the output of a radio receiver or are energized by alternating or pulsating currents in any well known manner. When the coils are energized, the soft iron armature 3 becomes ma etized, one end becoming a north pole an the other end a south pole, according to the direction of the current pulsation in the coils. When the right-hand end of the armature, as shown in Fig. 1, becomes a north pole, there is a force tending to move that end of the armature downward. At the same instant, a similar force tends to move the other end of the armature, which is at that instant a south pole, upward. The armature accordingly moves through a small arcin a clockwise direction about a pivot point corresponding to the connection between the armature 3'and the spring 4. When the polarity of the armature is reversed as a result of the current pulsation through the coils 5 being reversed, the armature movement is likewise reversed.

One end of the armature is connected through a rod 6, a lever 7 pivoted at a point 8, and a rod 9, to a cone or any other kind of diaphragm 10. If a small cone .is used, i.'e. a cone approximately six inches in diameter, the lever 7 should be a step-up lever, as is shown, but if a cone having a diameter of, say, fifteen to eighteen inches is used, the lever should be a step-down lever. In some cases the lever can be omitted and the cone or diaphragm can be connected directly to the rod 6. j I

According to one form of my invention,

the other end of the armature 3 is extended direction, the sides of the notch 13 will yieldto protrude past the pole points N and S as indicated at 11. A piece of rubber 12, having a notch 13 slightly larger than the end'of the armature, is secured in any manner such as by screws 14 and washers 15 to the pole pieces 1 and 2. The end 11 of the armature fits into the notch 13 so that upon a slight movement of the armature in either ingly engage the end of the armature. In this way the rubber member acts to damp the armature movement and also prevents the armature from striking the pole pieces.

In Fig. 3, a modification is shown in which the rubber member 12 is omitted. In this modification holes are drilled in the ends of th'e pole pieces 1 and 2 and small rods or bumpers of soft rubber, as shown at 16, are

placed in these holes so as to engage the armature member 3 when it moves toward the pole pieces. Set screws 17 are provided for adjusting these small rubber members 16.

While four of these rubber members have been shown, the operation would be practically the same if only two were used. The pair at either end of the armature 3, could be used or both of the rubber members in either of the pole pieces 1 and 2, will operate satisfactorily.

It is not necessary that rubber be used, as any yielding means, such-as felt or compression springs will work equally well. For example, it is merely necessary to substitute felt for the rubber in Figs. 1, 2 or 3. Felt or rubber are both effective in damping a resonance peak in the vibrating system. Compression springs, while not so effective in introducing damping at resonance points, do limit the amplitude of motion of the arma ture and tend to re-introduce stiffness or compressibility as the armature approaches the poles, thus preserving a uniform degre'e of stiffness in the vibrating system for all -positions of the vibrating armature. ithout the compression springs, the stiffness. becomes continuously less as the armature approaches the poles. The compression springs may be substituted for the rubber members 16 or theymay be arranged along the side ofthe pole pieces. 1 and 2 to abut the end of armature 3 in a manner similar to member 12. YVhen springs are usedit is advisable to fill the springswith cotton or felt fibres to prevent rattle of the spring.

Thereare various other modifications that can be made without departing from the spirit of my invention and I do not intend to be limited by the modifications shown but only by the scope of the appended claims.

What I claim is: v 1. In' combination a permanent magnet, a. pair of pole pieces on said magnet, an armature suspended for vibration between said pole pieces, one end of said armature protruding past said pole pieces, and means comprising a single slotted member fastened to said pole pieces and positioned to engage the end of said armature and limit its movements, said member being of yielding material and having a slot which'is larger than the end of the armature into which the end of the armature extends.

2. In combination a permanent magnet, a pair of pole pieces on said magnet, an armature suspended to vibrate between said pole pieces one end of said armature protruding past said pole pieces, a soft rubber member fastened to said pole pieces, and a slot ,in said rubber member slightly larger than the end of said armature, said rubber member being positioned so that the end of said'armature extends into said slot.

an elongated armature a. An electric acoustic deviop oon prising a U-sha d permanent magnet, a of pole pieces iz onnected to the ends of sal d fl-shaped v magnet each of said pole pieces having a portionwhichris U-shaped, said pole pieces being arranged so as to rovide a pair of air igaps across each of whi is a magneticfield,

spring supported in said air gaps, each end 0 said armature extending slightl beyond the portions of the pole pieces w ch define the air gaps, a-

dia hragm, means conn one end of said armature with said diap a strip of rubber having a. transverse slot out therein the width of said slot being greater than the thickness of said armature and less than the distance between the pole pieces which define said air means for adjustably sa'i strip of rubber to the legs. of said U-shaped pole pieces which define one of said air'g'aps in a manner such that the end of said armature which is not connected to said diaphragm extends into the slot cut in said strip of rubber and engages the sides of said slot upon movement of said armature whereby contact of said armature with said pole pieces is pre+ vented. ABRAHAM RINGEL.

rtions of said aps, and? 

